Torque on Electrical Fastener

Merry Christmas
T

tajalir

Member
Location
Florida
Occupation
Engineer
NEC Annex I provides torque values to use where the manufacturer did not specify the torque requirements. Table I-3 footnote refers to UL 486A-2003 for fasteners with multiple tightening means. Does anyone have this UL reference document? I am wondering what it says. I have a 10-32 grounding screw that can accommodate various types of tightening bits.
 
tajalir said:
Does anyone have this UL reference document?
Click to expand...
You can view all of the UL documents for free, but they use the same non-user friendly viewing system that the NFPA uses for their free viewing. Just like the NFPA, you need to register using an e-mail address.
 
I fail to see why type if driving tool used should change anything here when the fastener is designed for multiple driving tools.

The torque imposed on the fastener is what is doing the intended job here.
 
don_resqcapt19 said:
You can view all of the UL documents for free, but they use the same non-user friendly viewing system that the NFPA uses for their free viewing. Just like the NFPA, you need to register using an e-mail address.
Click to expand...
I greatly appreciate your directing me there. I did not know that UL would provide that for free, so I had not even tried.
 
kwired said:
I fail to see why type if driving tool used should change anything here when the fastener is designed for multiple driving tools.

The torque imposed on the fastener is what is doing the intended job here.
Click to expand...
Thank you for chiming in. don_resqcapt19 advised that UL standards are available to read for free. After reading the standard, I see that the torque values that NEC copies on Annex I are the UL test values. In other words, you prepare the specimen to be tested using these torque values. I think I can make some sense of why UL specifies the torque based on the type of screw head being used (as compared to the conductor being clamped). When you are tightening a screw with a hex head, you can apply a lot more torque than when you are using a slotted head screwdriver. And as the comments from other electricians in this thread indicate, the typical electrician does not carry a torque wrench. So a hex head will be potentially torqued to a much higher value than a slotted head in practice. And UL tests the connector that way. But the way that NEC references this table in Annex I is very confusing. It gives the impression that the table is providing a recommended torque value in the field (which was not the intent of UL 489 where the table came from).
 
tajalir said:
I think I can make some sense of why UL specifies the torque based on the type of screw head being used (as compared to the conductor being clamped). When you are tightening a screw with a hex head, you can apply a lot more torque than when you are using a slotted head screwdriver. And as the comments from other electricians in this thread indicate, the typical electrician does not carry a torque wrench. So a hex head will be potentially torqued to a much higher value than a slotted head in practice.
Click to expand...
They are talking about USING a torque wrench or screwdriver. I see nothing about hand tightening.

-Hal
 
herding_cats said:
here you go.
Click to expand...
Thank you for providing this table. It is different from what is in the NEC Annex I. I see that you took the table from an NEC handbook. It seems that the handbook replicated the exact table from UL 489, but the NEC code book has altered the table. Noticeably, on Table I-1 from the handbook you provided, the columns for Split bolt and Other Connectors are under a heading of Hex Head drives. In the NEC itself, the table crams them under slotted head screws, making a completely nonsensical situation. NEC Annex I really needs some work.
 
tajalir said:
Thank you for chiming in. don_resqcapt19 advised that UL standards are available to read for free. After reading the standard, I see that the torque values that NEC copies on Annex I are the UL test values. In other words, you prepare the specimen to be tested using these torque values. I think I can make some sense of why UL specifies the torque based on the type of screw head being used (as compared to the conductor being clamped). When you are tightening a screw with a hex head, you can apply a lot more torque than when you are using a slotted head screwdriver. And as the comments from other electricians in this thread indicate, the typical electrician does not carry a torque wrench. So a hex head will be potentially torqued to a much higher value than a slotted head in practice. And UL tests the connector that way. But the way that NEC references this table in Annex I is very confusing. It gives the impression that the table is providing a recommended torque value in the field (which was not the intent of UL 489 where the table came from).
Click to expand...
Isn't one the first reasons we need to tighten to a certain level is to accomplish a reliable connection from the conductor to the termination device?

If everything about two different terminations is the same other than one is hex head and the other one is slot head, don't we still need the same pressure bearing down on the conductor to get the same performance out of both of them? If the slot head design has more trouble giving the amount of torque needed then maybe it is a poor design choice for that particular termination device.

If the device has a combination type head that can be driven by more than one type of tool, don't you still want the same pressure on the conductor you are terminating regardless which tool you decide to use to get the correct performance out of the assembly?
 
You must log in or register to reply here.
Top